1. Field of the Invention
This invention relates to motion sensitive valves and in particular to shut-off valves for use in the event of seismic disturbances.
It is well known that earthquakes and other disturbances can displace gas, water and utility lines, causing breakage or rupture, which leads to subsequent damage due to leakage or fire. Attempts have been made in the past to provide safety cut-off valves for controlling for example the flow of natural gas after line rupture. For the most part, these attempts have not been successful in providing a safety device of simple, inexpensive, reliable and rugged construction capable of being installed on existing mains without the need to insert inline valves. These limitations have severely limited the acceptance of inertially triggered devices in spite of an obvious need for such devices.
One of the principal problems associated with inertially actuated devices is a trigger mechanism capable of satisfying strict seismic response requirements. For example, the American National Standard for Earthquake Actuated Automatic Gas Shut-off Systems (ANSI Z21.70-1981) specifies that the sensing means of a valve or system shall actuate the shut-off means within five seconds when subjected to a horizontal sinusoidal oscillation having a peak acceleration of 0.3 G and a period of 0.4 second. Furthermore, the sensing means shall not actuate the shut-off means when subjected for five seconds to horizontal sinusoidal oscillations having a peak acceleration of 0.4 G with a period of 0.1 second or a peak acceleration of 0.08 G with a period of 0.4 second or a peak acceleration of 0.08 G with a period of 1.0 second. These specifications thus require that the trigger mechanism be effective for a 2.5 Hz oscillation with 0.3 G of force and substantially immune to oscillations outside of a narrow frequency range or a low force level.
In the past, a number of valving solutions have been suggested for use in fluid systems, particularly in natural gas systems. The typical solution requires that the gas line be cut, junctions be threaded and a coupling be inserted in the line containing the seismic-actuated valve. These solutions have proved unsatisfactory for a number of reasons. First, it is particularly undesirable to disturb a gas line in any way because of the risk of leakage. Second, the cost of installation of such a valve can be substantial, since most local building codes require that the installation be subject to inspection and/or be performed by a certified plumber.
State-of-the-art automatic shut-off valves have been found to be unreliable due to false triggering or sticking. As such, such valves are not widely accepted or even recommended by utility companies, particularly gas utility companies.
What is therefore needed is a seismic actuation system and in particular an inertially triggered fluid flow valve control system which can be installed externally of the gas line, operate on existing valves in the gas line, and be able to operate reliably and according to specification.
2. Description of the Prior Art
Line-insertable mechanisms are known which satisfy nationally accepted standards. These mechanisms are generally valves intended to be inserted in gas lines and require professional installation. For example, Koso International of Los Angeles, Calif. manufactures an earthquake actuated shut-off valve approved by the Architectural Board of the State of California. The Koso California (Brand) Valve employs a rolling latch in a cup to hold open a biased valve. The rolling latch is a heavy metal sphere of a first diameter in a cup of a second diameter which is actuated when the sphere is forced from the cup by seismic oscillation.
Another example of a shut-off valve which employs a rolling latch is Paulson U.S. Pat. No. 4,185,651.
Automatic shut-off valves are known which are intended to close the inline plug cock on the gas main. U.S. Pat. No. 3,791,396 to Nelson discloses a shut-off mechanism which employs a spring under tension coupled to a lever mounted to the stem of the plug cock. The Nelson patent employs a weight having a tapered base mounted in a metastable position on a platform. When disturbed, the weight topples thereby pulling upwards on a chain and causing a latch assembly to effect the release of a lever extension with the resulting closing of the plug cock valve. The Nelson device cannot fit in small spaces because it must be mounted along a substantial length of gas pipe and must employ a powerful spring attached to a lever on the plug cock. Furthermore, the trigger mechanism is susceptible to failure due to binding in the latch assembly from the high forces of friction and the high pressures exerted on the valve lever. The Nelson patent has the further disadvantage of requiring that the latch be able to withstand substantially the same pressure exerted on the lever.